1. FIELD OF THE INVENTION
The present invention relates generally to the mixing of small quantities of fluid samples in sealed containers such as vials or sealed test tubes and, more particularly, to the mixing of biological specimens, such as blood, prior to the withdrawal of samples for biological testing.
2. DESCRIPTION OF THE PRIOR ART
The in vitro diagnostic testing of samples of whole blood or certain constituents thereof such as the differential counting of the various types of leukocytes (white blood cells) has long been a valuable medical tool in determining the presence of disease or other abnormalities in both man and animals. Such tests usually involve small quantities of blood taken from the specimen withdrawn from a patient. In order for test results to be reliable, the samples used must be as representative of the patient's blood as possible.
Generally, a specimen of blood withdrawn from a patient is placed in a sealed vial or test tube containing an amount of an anti-coagulant and/or a fixative or other preservative agent. Test samples are then withdrawn from the larger specimen as needed.
Because unmixed whole blood has a tendency to separate into layers of its constituents, in order for any subsequent sample withdrawn from the specimen to be representative of the original, the original sample must be thoroughly mixed and is preferably maintained in an agitated state.
Several types of devices have been used to maintain biological samples such as whole blood in homogenized condition. One such prior art device is illustrated and described in U.S. Pat. No. 3,747,900 to Dilts dated July 24, 1973. That device comprises d.c. motor-driven, vertical plate to which clips for holding tubes or vials containing the fluid to be mixed are attached by permanent magnets or adhesive nylon strips. Another such prior art device which utilizes an adjustably tiltable, motor-driven rotating disc member having a plurality of vial or test tube holding clips permanently secured thereto is disclosed in U.S. Pat. No. 3,163,404 to Kraft, et al., dated Dec. 29, 1964.
While both of these prior art devices may successfully mix fluids, they suffer from several disadvantages. Generally the clips can accommodate tubes only of a specified diameter, and after a time the clips lose their resiliency and must be replaced. The necessity of using clips at all increases the amount of handling required because the vials or tubes must be inserted and removed from the clips. This, of course, increases the likelihood of vial or tube breakage. Also, in the case of permanently attached clips, it is quite difficult to add or remove tubes to the disc while the disc is operating.